Direct current double air gap motor



Dec. 6, 1966 K. ADLER ETAL 3,290,528

DIRECT CURRENT DOUBLE AIR CAP MOTOR Original Filed May '7, 1963 2Sheets-Sheet 1 116.1 FIG. 2

m 1s a 12 1 12g 1 I I 5 1 2 i 5 5 Q 1 11 1o INVENTORS MKM ATTORNEYS D66.6, 1966 ADLER T 3,290,528

DIRECT CURRENT DOUBLE AIR CAP MOTOR Original Filed y 1963 2 Sheets-Sheet2 FIG."-

FIG.5 32

INVENTORS Karl Hdler and Georges nucommun BY 976M44 ATTO RNEYS UnitedStates Patent 3,290,528 DIRECT CURRENT DDUBLE AIR GAP MUTUR Karl Adler,Ruti, Buren, and Georges Ducommun,

Grenchen, Switzerland, assignors, by mesne assignments, to BiviatorS.A., Geneva, Switzerland, a corporation of Switzerland Continuation ofapplication Ser. No. 278,731, May 7, 1963. This application Mar. 8,1966, Ser. No. 536,553 Claims priority, application Switzerland, May 12,1962, 5,69fi/ 62 9 Claims. (Cl. 310-266) This application is acontinuation of Serial No. 278,731, filed May 7, 1963, now abandoned.

This invention relates to a direct current micro motor adapted to startup and to deliver mechanical energy with extremely small availableelectrical power. As an example, the motor is able to wind up atimepiece when connected to a battery of photoelectric cells having asize in the order of 75 cm. and exposed to an illumination of 10 lux.Extensive experiments have shown that under these circumstances a usefuloutput is only obtained if a number of conditions are fulfilled, wherebythe general disposition of the micro motor substantially differs of theusual structure of direct current motors. Care must be taken that theavailable current is always used most efficiently for producing adriving turning moment, this being impossible with classical directcurrent motors comprising series-connectedrotor windings.

The micro motor according to this invention broadly comprises acommutator, separate windings of diametral pitch electrically isolatedfrom each other and having winding ends connected to diametricallyopposite commutator segments of the commutator, magnetizable meansincluding a permanent magnet forming an air gap for accommodation ofwinding portions, brush means cooperating with said commutator foralternatively and successively connecting one of said windings to saidbrush means for feeding said one winding with direct current, saidmagnetizable means being formed to produce a homogeneous magnetic fieldin said air gap of such a circumferential extension that each winding iscompletely within said homogeneous field for any position wherein it isconnected to said brush means. Under these conditions allcurrent-carrying conductors of all windings will always be within thepractically homogeneous magnetic field and will fully add to theproduction of the turning moment of the motor. When using a statorcomprising the said permanent magnet, the pole pieces and themagnetizable core of the stator will preferably be shaped in such a waythat all magnetic field lines of the homogeneous field extend in radialdirection so that the electro-mechanical forces acting onto theconductors of the rotor windings always have a substantiallycircumferential direction and thus produce a maximum turning moment. Inorder that the above conditions may be fulfilled, it is preferable touse windings of which the circumferential length is smaller than anyother dimension of the windings.

Two embodiments of the invention are shown, by way of example, in theattached drawings wherein:

FIG. 1 is an axial section of the first embodiment,

FIG. 2 shows the motor partially in elevation and partially in section,along line II-Il in FIG. 1,

FIG. 3 is a schematic illustration of the commutator and brush means ofthe motor,

FIG. 4 is an axial section of the second embodiment and FIG. 5 is across section of the second embodiment.

The bearing brackets or plates 1 and 2 are provided with jewels 3 and 4.Jewel 4 may be adjusted in axial direction by means of a screw 5. Thebearing plate 2 is directly connected to the pole pieces 7 of the motorwhereas a ring 6 is inserted between bearing plate 1 and the pole pieces7. As shown in FIG. 2 the pole pieces 7 are made in one piece with yokes3. A permanent magnet 9 is inserted between yokes 3.

The bearing plate 2 has a tubular extension 10 carrying a soft iron core11 made of magnetizable material having as low electrical conductivityas possible in order to avoid eddy currents in this core. The motorshaft 12 is pivoted in bearings 3 and 4 by means of ground pivots. Theshaft extends through bores of the extension 10 and of core 11. Awinding body or rotor 13 of substantially cylindrical shape is fixed onshaft 12. An axial extension 14 of rotor 13 forms the support of thecommutator 15.

The Winding body or rotor 13 comprises four slots 16 having acircumferential width less than A of the rotor circumference. The rotor13 is made of plastic material of any other suitable non-magnetizableinsulating material. Axially extending portions of two windings 17 ofdiametral pitch and arranged in mutually perpendicular planes areaccommodated in slots 16. The winding portions outside the slots 16 aresupported on the cylindrical end portions of rotor 13 and thus are ofsubstantially circular shape concentric to the motor shaft 12. By thisarrangement of the winding portions outside the slots 16 electromagneticforces acting in circumferential direction on such winding portions dueto stray flux are avoided. Windings 17 are completely insulated fromeach other and the terminals of each winding are connected todiametrically opposite commutator segments.

Two brush holders 18 of insulating material support each a pair ofcontact springs 19 of an elastic nonoxydizable gold alloy. The contactsprings or brushes 19 of each pair enclose a small angle substantiallycorresponding to the angular distance or angular width of the gapbetween adjacent commutator segments. By this arrangement current flowin at least one winding is obtained for any position of the gaps betweencommutator segments relatively to the contact springs 19. Each pair ofbrushes 19 is connected to one terminal of a direct current source.

Within a hollow space of the bearing plate 2 a pinion 20 is fixed on themotor shaft 12, this pinion meshing with a wheel of a reduction gear notshown in the drawing. The reduction gear may include a return stop andmay serve for rewinding a timepiece.

The operation of the motor shown in FIGS. 1 to 3 is as follows: When therotor 13 takes the position shown in FIG. 2, the commutator is in itsneutral position shown in FIG. 3. The one winding 17 that has previouslybeen energized will now be disconnected from the brushes and the currentwill be fed to the other winding, whereby both windings may becurrent-carrying for a short time. As shown in FIG. 2 the slots 16 andthe winding spaces of windings 17 respectively and the circumferentiallength of the pole pieces 7 are so disposed that for the illustratedneutral position all conductors of both windings 17 are fully within apractically homogeneous magnetic field set up between the pole pieces 7and the core 11, so that the total current flow in all conductors of thewindings fully contributes to the driving turning moment. When thepreviously energized winding is disconnected the full current flow iscarried by one winding which will fully remain in the homogeneousportion of the magnetic field during its energization, that is for arotating angle of about Since all conductors of both windings arecompletely within the homogeneous portion of the magnetic field producedin the air gap for the neutral position shown in FIG. 2, it is evidentthat all conductors of each winding are within the homogeneous field aslong as the Winding is connected to the current source. Conse quently,each Winding will produce a constant maximum turning moment for its fullcurrent-carrying periods. Due

to this fact, a substantially constant speed of the rotor is obtained,this being important for making optimal use of the available electricenergy because the counterelectromotive force is practically constantunder the conditions specified above. A continuous optimal matchingbetween the apparent resistance souroe voltagecountereleetromotive forceand the source is thus possible (wherein I is the current). Thispossibility is of particular importance where the motor is energized bya photoelectric battery because an optimal working point may be adjustedfor the battery and the motor, this working point remainingsubstantially constant.

In order to obtain the said practically homogeneous radial field in theair gap of the stator it is preferable to choose an air gap length, thatis a radial distance between the inner surfaces of the pole pieces 7 andthe core 11, substantially less than the shortest distance betweenopposite pole pieces. Under these conditions it is equally possible toavoid excessive stray flux and to make good use of the availablemagnetic flux.

It was found that the stray flux Within reach of the winding portionsoutside the pole pieces 7 and the core 11 respectively should be kept aslow as possible in order to avoid breaking moments. One importantfeature for reducing this stray flux consists in the arrangement of thepole pieces 7, the yokes 8 and the magnet 9 in a common symmetry planeperpendicular to the motor shaft. For obvious reasons the main portionof the stray flux will be parallel to the said common symmetry plane andwill thus be without effect on the winding portions axially projectingfrom the air gap. 7

The following table shows the dimensions and characteristics of a motorof the type described above suitable for operation at a voltage of 0.12volts and 50 microamperes produced by a photoelectric battery. Thispower may for instance be produced by a battery of sixseleniumphotocells connected in parallel and having a total surface of75 cm. exposed to an illumination of 10 lux. The motor is able to rewindthe spring of a high quality timepiece at an illumination of 20 luxwithin hours.

Voltage volts .12 Current A .00005 Induction in air gap gauss 750Conductors per winding 950 Length of conductors cm 1.6 Circumferentialspeed of rotor cm./sec 5.3 Speed r.p.m 60 Rotor diameter cm 2 Corediameter cm 1.35 Core length cm.. 1.6 Pole length cm 1.6 Pole diameter"cm" 2.25 Pole distance cm 1.3 Air gap length cm .45 Total force on bothwinding sides gr 0114 Turning moment gr./cm .0114 Electromotive forcevolts .114 Rotor resistance ohms 120 Conductor diameter mm .12

- magnet. The permanent magnet should also have low electricalconductivity in order to avoid eddy current losses in this magnet.Instead of a rotor carrying the windings the permanent magnet of such amotor may be fixed on the motor shaft and stationary windings may beaccommodated il 1 5 air gap, such windings being alternatively energizedby collector means associated therewith. In this case the size andweight of the windings is not limited by the necessity of accommodatingthem on the rotor so that higher turning moments may be obtained. Itwould be easier to accommodate a higher number of individual windings.

A motor having a permanent core is shown by way of example in FIGS. 4and 5. Parts of this motor are designated with the reference numeralsused for analogous parts in FIGS. 1 to 3.

The motor shown in FIGS. 4 and 5 has a permanent magnet 20 carrying polepieces 21 having cylindrical external surfaces. Magnet 20 is fixed on abase 22 of plastic material by means of pins 23. The other end of magnet20 has a cylindrical recess 24. A hearing carrier 25 is inserted in thisrecess, this body serving for accommodation of jewels 26 and 27 for themotor shaft 28. The rotor 13 and commutator 15 fixed on shaft 28 and thewindings 17 accommodated on the rotor correspond in every practicalrespect to the same parts shown in FIGS. 1 and 2. The same applies forthe brush holders 18 and brushes 19. The brushes of each pair arearranged at an angle of 20, this resulting in a working angle of thewindings, that is an angular range wherein each winding is continuouslyconnected to the current souce, of The brush holders and a bearing 29,30 for the motor shaft are fixed on a bearing bracket or hearing plate31. The base 22 and the bearing plate 31 are assembled with a soft ironmantle 32 having an axial length equal to the axial length of the magnet20 and pole pieces 21 respectively.

A homogeneous magnetic field is formed in the air gap between the polepieces 21 and the soft iron mantle 32, whereby the circumferentialextension of each side of the homogeneous field substantiallycorresponds to the circumferential extension of the cylindrical surfacesof the pole pieces 21. As stated above in connection with the embodimentshown in FIGS. 1 and 2 the circumferential extension of the homogeneousfield portions is so chosen that each conductor of any current-carryingwinding is completely within this homogeneous field portions during itsfull working angle, that is during each full period of continuouscurrent flow in a winding. As stated above, the working angle is 110 andsince the circumferential length of each winding is in the order of 45,the homogeneous field portions should extend through an angle of atleast In the embodiment shown in FIGS. 4 and 5 the above conditions areobtained when the distance D between the pole pieces 21 is 4 mm. with aradial width of the air gap of 2.65 mm. With these conditions the strayflux between the pole pieces may be kept within reasonable limits, butit is preferable to increase the distance 'between pole pieces 21 asmuch as possible as long as the fundamental condition may be fulfilledthat all current-carrying conductors of any winding will be with in asubstantially homogeneous portion of the magnetic field.

Since the overall dimensions of the micro motor and consequently thedimensions of the permanent magnet 20 are relatively small it is ofparticular importance not to reduce the volume of the magnet. shown inFIGS. 4 and 5 a central bore of the permanent magnet is avoided by thefact that the motor shaft is pivoted substantially at one side of thepermanent magnet so that the reduction of the magnet volume is limitedto the fixing holes taking up pins 23 and to the recess taking up thebearing body 25. Further, since the motor shaft is completely outsidethe magnetic field no magnetic pulls in radial direction due to slightasymmetries of the motor shaft will occur, this being of importance foran absolutely indifierent and smooth operation of the motor.

While this invention has been described with reference to specificembodiments, other modifications are possible within the scope of theattached claims. As an example In the embodiment the dimensions andcharacteristics of the motors may be modified within relatively widelimits. The number of conductors of the windings may be chosen between500 and 1200 whereby the induction in the air gap should be inverselyproportional to the number of conductors in order to obtaincorresponding characteristics.

What is claimed is:

1. A direct current motor comprising a rotor including a substantiallycylindrical carrier, a plurality of multiple layer windings each windinghaving turns lying in diametrical planes of the carrier and whoseopposite sides are embedded therein so that the outer turns are flushwith the outer surface of the carrier, and a commutator having pairs ofdiametrically opposed conductive segments, opposite ends of each windingbeing connected each to one segment of one of said pairs of segments,each said winding and connected segments of the commutator subtendingsubstantially the same angle of rotor displacement, brush means arrangedto contact one of said pairs of segments to connect the segments of eachpair to a direct current source during displacement of the rotor throughsaid angle, and a flux conducting stator including permanent magnetmeans, a cylindrical member and a pair of opposed pole pieces havingcylindrical surfaces each subtending an are at least equal to the sum ofthe arcs subtended by two adjacent windings, said cylindrical member andpole piece cylindrical surfaces being coaX-ially positioned to define anannular air gap between them, said carrier and windings being disposedin and angularly displaceable through said air gap, the width of saidair gap being less than the shortest distance be tween said pole piecesto reduce stray flux and provide homogeneous magnetic flux fields ofsubstantially constant flux density in said air gap between each polepiece and the cylindrical member, whereby each said winding whileconnected to a direct current source through a pair of commutatorsegments and said brush means is completely inside one of saidhomogeneous flux fields during the total time of displacement of therotor through said angle.

2. A direct current motor according to claim 1 wherein a pair ofwindings is provided lying in mutually perpendicular diametrical planesof the carrier.

3. A motor according to claim 1 wherein said brush means comprisingpairs of brushes including contact springs of gold contacting saidcommutator on diametrically opposite segments thereof, the brushes ofeach pair enclosing an angle slightly exceeding the angular distancebetween adjacent commutator segments.

4. A direct current motor according to claim 3 wherein said windings aretwo in number connected to four of said conductive commutator segments,and the brushes of each pair of brushes are arranged at an angle ofapproximately 20.

5. A direct current motor according to claim 4 wherein said permanentmagnet means comprises a permanent magnet outside said rotor, yokes ofmagnetized material connected to said permanent magnet and enclosingsaid rotor, said yokes terminating in said pole pieces having polesurfaces of cylindrical shape, and said cylindrical member being a coreof soft iron inside said winding carrier.

6. A direct current motor according to claim 1 wherein said homogeneousflux fields have a flux density in the order of 750 gauss.

7. A direct current 'motor according to claim 1 wherein said permanentmagnet means comprises a permanent magnet of prismatic shape havingopposite ends contacting said pole pieces, said pole pieces and saidcylindrical member being made of soft iron, both said permanent magnetand pole pieces being disposed within said rotor.

8. A direct current motor according to claim '7 wherein said permanentmagnet of prismatic shape is fixed against rotation with the rotor, saidpole pieces having inner flat surfaces contacting flat opposite endsurfaces of said permanent magnet.

9. A direct current motor according to claim 8 wherein said cylindricalcarrier has a closure wall at one end which overlies one end of saidprismatic permanent magnet, a bearing recess in said one end of theprismatic magnet, a shaft mounting said commutator and winding carriersupported at one end in said bearing recess and having its other endrotatably supported in a bearing plate spaced on the other side of saidclosure wall from said one end of the permanent magnet.

No references cited.

MILTON O. HIRSHFIELD, Primary Examiner. l. GIBBS, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No I 3, 290528 December 6, 1966 Karl Adler et a1.

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 6, line 10, for the claim reference numeral "4" read 1 u Signedand sealed this 26th day of September 1967.

(SEAL) Attest:

ERNEST W. SWIDER Attesting Officer EDWARD J. BRENNER Commissioner ofPatents

1. A DIRECT CURRENT MOTOR COMPRISING A ROTOR INCLUDING A SUBSTASNTIALLYCYLINDRICAL CARRIER, A PLURALITY OF MULTIPLE LAYER WINDINGS EACH WINDINGHAVING TURNS LYING IN DIAMETRICAL PLANES OF THE CARRIER AND WHOSEOPPOSITE SIDES ARE EMBEDDED THEREIN SO THAT THE OUTER TURNS ARE FLUSHWITH THE OUTER SURFACE OF THE CARRIER, AND A COMMUTATOR HAVING PAIRS OFDIAMETRICALLY OPPOSED CONDUCTIVE SEGMENTS, OPPOSITE ENDS OF EACH WINDINGBEING CONNECTED EACH TO ONE SEGMENT OF ONE OF SAID PAIRS OF SEGMENTS,EACH SAID WINDING AND CONNECTED SEGMENTS OF THE COMMUTATOR SUBTENDINGSUBSTANTIALLY THE SAME ANGLE OF ROTOR DISPLACEMENT, BRUSH MEANS ARRANGEDTO CONTACT ONE OF SAID PAIRS OF SEGMENTS TO CONNECT THE SEGMENTS OF EACHPAIR OF A DIRECT CURRENT SOURCE DURING DISPLACEMENT OF THE ROTOR THROUGHSAID ANGLE, AND A FLUX CONDUCTING STATOR INCLUDING PERMANENT MAGNETMEANS, A CYLINDRICAL MEMBER AND A PAIR OF OPPOSED POLE PIECES HAVINGCYLINDRICAL SURFACES EACH SUBTENDING AN ARC AT LEAST EQUAL TO THE SUM OFTHE ARCS SUBTENDED BY TWO ADJACENT WINDINGS, SAID CYLINDRICAL MEMBER ANDPOLE PIECE CYLINDRICAL SURFACES BEING COAXIALLY POSITIONED TO DEFINE ANANNULAR AIR GAP BETWEEN THEM, SAID CARRIER AND WINDINGS BEING DISPOSEDIN AND ANGULARLY DISPLACEABLE THROUGH SAID AIR GAP, THE WIDTH OF SAIDAIR GAP BEING LESS THAN THE SHORTEST DISTANCE BETWEEN SAID POLE PIECESTO REDUCE STRAY FLUX AND PROVIDE HOMOGENEOUS MAGNETIC FLUX FIELDS OFSUBSTANTIALLY CONSTANT FLUX DENSITY IN SAID AIR GAP BETWEEN EACH POLEPIECES AND THE CYLINDRICAL MEMBER, WHEREBY EACH SAID WINDING WHILECONNECTED TO DIRECT CURRENT SOURCE THROUGH A PAIR OF COMMUTATOR SEGMENTSAND SAID BRUSH MEANS IS COMPLETELY INSIDE ONE OF SAID HOMOGENEOUS FLUXFIELDS DURING THE TOTAL TIME OF DISPLACEMENT OF THE ROTOR THROUGH SAIDANGLE.